The 70% ethanol wash is intended to remove salt. You can do that more than once if you need to, since the DNA is insoluble in the wash. Make sure you really have 70% rather than 95%, since the salt will not dissolve in 95% EtOH.

I would add a chloroform only extraction before the ethanol precipitation. You may be carrying over phenol into your sample. I don't understand why you think there is salt in your sample. What evidence is there for this?

I would add a chloroform only extraction before the ethanol precipitation. You may be carrying over phenol into your sample. I don't understand why you think there is salt in your sample. What evidence is there for this?

Could you explain "why you think phenol is cause of salt"I attach picture before centrifugeAfter that it has many salt

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It's hard to tell from only the picture, but I'm guessing that you are picking up protein and other junk from the phenol/chloroform extraction. After you centrifuge, you should have a clear layer on top and a white layer in the middle, with (perhaps) a clear layer underneath. You want to take just the clear top layer, avoiding everything else. Don't try to get it all, at least for now.

It also looks as if you might have far too much sample for the amount of phenol/chloroform you are using. You might scale the sample back by 10x and try again, or use a bigger tube and add more phenol/chloroform.

It's hard to tell from only the picture, but I'm guessing that you are picking up protein and other junk from the phenol/chloroform extraction. After you centrifuge, you should have a clear layer on top and a white layer in the middle, with (perhaps) a clear layer underneath. You want to take just the clear top layer, avoiding everything else. Don't try to get it all, at least for now.

It also looks as if you might have far too much sample for the amount of phenol/chloroform you are using. You might scale the sample back by 10x and try again, or use a bigger tube and add more phenol/chloroform.